Current indoor heating systems are inefficient and expensive, heating the whole room in order to heat the people inside it, so that a person can move around freely within that space. Both forced hot air and hydronic systems (circulating hot water or steam, such as baseboard heaters, used extensively in the northern United States) heat mostly via convection, which is very inefficient. They heat the air, which circulates and eventually heats up points of need (PONs) and all objects in the room. Hot air rises, so the warmest part is usually the ceiling, the most unutilized part of the environment. Hydronic systems are often called radiators however they are principally convection devices with only a small portion of the energy being transferred by radiation. This radiation component heats objects directly without warming the air in between, such as electric oil-filled heaters where the oil is heated and circulated within a device that has fins to distribute heat from the device. The radiation is therefore poorly used with the energy decreasing exponentially with the distance from the source because it spreads in all directions: this is the inverse square law of Physics. Other heating systems such as radiant floor heating systems provide an improvement because the temperature decreases with height, where the warmth is near the bottom of a room and is colder as you go higher, thus most of heat stays in a utilized area. This is better than convective systems because the temperature decreases with height, thus most of it stays—closer to the floor. The systems are therefore considered to have a good temperature profile where the heating is stable (the floor acts as a thermal store), but the system still heats the entire floor and room and does not take into consideration where an occupant is; furthermore, it typically takes time for the floor to warm up and cool down, so there is a latency. Note that some convection is also created by this type of heating. Radiant floor heating is also expensive to install.
Other systems such as Electric Thermal Stores (ETS) use electricity to heat an object such as ceramic bricks or certain inorganic salt solutions. These materials have a very high capacity to store energy (Thermal Mass) and then release it when unplugged. They are useful when daytime (peak) electric tariffs are higher than nighttime (off-peak). The ETS is plugged in during the night to charge and unplugged during the day to discharge the heat. These have been in use in Europe since the 1940s, but aren't common in the United States except in some rural electric cooperatives where dual tariffs exist. An ETS, thus, transfers energy temporally, i.e. over time, in addition to transferring it spatially. Additionally, “Near-zero” energy technologies exist to heat homes and offices that take advantage of insulation, shading, heat exchange with the outside, solar panels, wind turbines, etc., but each system requires expensive reengineering if not a complete redesign of the building. Various other devices, such as thermostats learn the user's behavior pattern exist, but are also expensive and ultimately use the existing heating system of the house or office, which can be an inefficient component. These devices do offer some savings by creating a heating plan that adapts as the person's usage changes and some systems provide home networking products specifically designed for controlling appliances.
Other heating systems, such as portable electric heaters or outdoor radiant heaters used at bus stops, hotel entrances and restaurants (whether gas or electrically powered) are efficient, but only if the person sits and remains in close proximity to the device. In any of these systems, the radiation is poorly used where the radiant energy decreases exponentially with distance from the source as it spreads in all directions, the inverse square law of Physics, and where areas are heated where there are no people. These systems therefore waste energy heating these areas where in general it takes a 1500 W heater to make a 10′×10′ room comfortable in winter.
Fans are also used with some radiant heaters to help circulate air faster, thus improving convection and increasing the range of heat delivery. There are various fan and heating element designs but they all depend on raising the temperature of air by forcing it under pressure over or through heated elements to transfer the heat. The air is then blown out of the device. Hot air can dry out the environment.
Taking into consideration that skin absorbs electromagnetic infrared (IR) radiation at wavelengths from 780 nm to 1 mm, which is felt as heat, an IR-A wavelength range of between 780 nm to 1400 nm centered on 1,000 nm provides the best sensation of heat as it has greater penetrating power. This means that the heat is dissipated in a larger skin volume, creating more pleasant and diffuse warmth. For example, the average male adult human has a surface area (skin) of two square meters, front and back with approximately 75% of the body heat loss (or gain) is from radiation. While average body temperature is 36.67° C./98.4° F. internally the human body generates about 130 W (watts) of power and needs to lose this power to the environment so that we don't overheat. For us to feel comfortable, neither cold nor hot, the ambient temperature should be about 26° C./78° F. at desirable humidity levels of between 30% to 60%. Forced air heating systems tends to dry the air out effecting desirable humidity levels and our feeling of warmth. If a thermostat is maintained at 20° C./68° F., the temperature at the body needs to be elevated by 6° C./10° F. to get to the comfortable 26° C., which takes 68 W for the entire body, or 3.4 mW/cm2 (milliwatts/square centimeter). Thus, at this point of need (PON) it takes 34 W to heat one side of the body or 11 W to heat one-third of the front of the body, assuming that the other two-thirds is covered by clothing. Thus, a system that transfers heat directly to the points of need (PONs) with the freedom of mobility and targeted efficiency would be desirable.